1. Field of the Invention
The present invention relates generally to an image sensor driving method and an electronic camera, and more particularly to an image sensor driving method suitable for a digital camera, etc. loaded with an image sensor with more than one million pixels, and an electronic camera using this image sensor driving method.
2. Description of Related Art
An image sensor of a conventional digital camera has a relatively small number of pixels such as 640xc3x97480. Then, the image sensor can be always driven by the same driving method, in which signal electric charges are read from all the pixels of the image sensor, during performing an automatic focusing (AF) and an automatic exposure control (AE) and at any mode such as a normal image-capturing mode and a macro image-capturing mode. This is called a normal driving.
A digital camera has been developed, which has many pixels to achieve a high quality image. With the increase in the number of pixels, the signals cannot be processed on time at the AF and AE in the normal driving method. To address this problem, there is proposed a method of driving the image sensor by reading the signal electric charges from xc2xd or xc2xc of the pixels at the AF and the AE. More specifically, the signal electric charges are read from every second or every fourth of pixels arranged vertically.
A refresh rate can be increased in the above-mentioned driving method in which the number of the pixels to be read is reduced in the vertical direction. The image data, however, can be missing in the vertical direction. Thus, it is impossible to accurately confirm whether an image is focused or not in the macro image-capturing mode. Moreover, if the image data are outputted to an outside monitor, a rough image is displayed on the monitor.
In view of the foregoing, it is an object of the present invention to provide an image sensor driving method in which images are refreshed at a high refresh rate in a normal image-capturing mode and at AE/AF, and an image with many pixels is captured in a macro image-capturing mode and when image signals are outputted to an external monitor; and an electronic camera employing such a method.
To achieve the above-mentioned object, the present invention is directed to an image sensor driving method for reading signals from photoelectric elements in an image sensor built in an image-capturing apparatus, the method comprising the steps of: reading signals from a first proportion of the photoelectric elements in the image sensor in a first mode; and reading signals from a second proportion of the photoelectric elements in the image sensor in a second mode, the second proportion being higher than the first proportion and up to all. For example, the first mode is a normal image-capturing mode; and the second mode is one of a macro image-capturing mode and a mode for outputting an image signal representing an image captured by the image sensor to external equipment.
According to the present invention, the image sensor is driven by reading the signals from the first proportion of the photoelectric elements in the normal image-capturing mode. In this case, the images can be captured at a high refresh rate, and the captured images are rough but satisfactory for confirmation of a picture composition as far as the images are displayed on a compact monitor, etc. attached to the image-capturing apparatus.
In the macro image-capturing (close range image-capturing) mode, the image sensor is driven by reading the signals from more photoelectric elements (the second proportion of the photoelectric elements) up to all the photoelectric elements. This captures the data of more pixels than in the normal image-capturing mode to thereby enable the accurate confirmation of the focus. Whether the image-capturing apparatus has the macro image-capturing mode or not, the number of the photoelectric elements to be read is increased to the second proportion up to all the photoelectric elements even in the normal image-capturing mode if the image-capturing apparatus is connected to the external equipment. Consequently, if the captured image is outputted to the external equipment such as a large-screen monitor, a precise image can be displayed on the monitor.
Preferably, in the image sensor driving method, a refresh rate of images captured by the image sensor in the first mode is equal to a frame frequency in a preset color television signal format. The preset color television signal format may be one of NTSC, PAL and SECAM.
This eliminates the necessity of storing the image captured by the image sensor into a frame memory. It is therefore possible to shut off the power of the frame memory, etc., and this does not waste the electricity.
To achieve the above-mentioned object, the present invention is directed to an electronic camera comprising: an image sensor for capturing an image, the image sensor including a plurality of photoelectric elements; an image display for displaying the image captured by the image sensor; a mode switcher for switching modes between a first mode and a second mode; and an image sensor drive controller for reading signals from a first proportion of the photoelectric elements in the image sensor in the first mode, and reading signals from a second proportion of the photoelectric elements in the image sensor in the second mode, the second proportion being higher than the first proportion and up to all. For example, the first mode is a normal image-capturing mode; and the second mode is one of a macro image-capturing mode and a mode for outputting an image signal representing an image captured by the image sensor to external equipment.
According to the present invention, the image sensor is driven by reading the signals from the first proportion of the photoelectric elements in the normal image-capturing mode. When the mode switcher sets the macro image-capturing mode, the image sensor is driven by reading the signals from more photoelectric elements or all the photoelectric elements automatically. This makes it possible to capture the images with many pixels in the macro image-capturing mode, so that the focus can be confirmed accurately.
Preferably, the electronic camera further comprises: an output interface for outputting an image signal representing the image captured by the image sensor to external equipment; and wherein the image sensor drive controller reads signals from a third proportion of the photoelectric elements in the image sensor in a mode for outputting the image signal to the external equipment through the output interface, the third proportion being higher than the first proportion and up to all. The third proportion may be equal to the second proportion.
When the electronic camera is connected to the external equipment, the number of the photoelectric elements to be read is increased or all the photoelectric elements are read even in the normal image-capturing mode. For this reason, the high-quality image can be displayed on the external image display apparatus. This is particularly advantageous when an external monitor with a large screen is used.
Preferably, the electronic camera further comprises: a high-quality image confirmation mode setting device for setting a high-quality image confirmation mode in response to an operation from outside; and wherein the image sensor drive controller reads signals from a third proportion of the photoelectric elements in the image sensor in the high-quality image confirmation mode, the third proportion being higher than the first proportion and up to all. The third proportion may be equal to the second proportion.
The electronic camera can be set to the high-quality image confirmation mode if the user operates a predetermined control part as the need arises. If the user selects the high-quality image confirmation mode in the normal image-capturing mode, the number of the photoelectric elements to be read is increased or the signals are read from all the photoelectric elements unconditionally. Therefore, the user can freely select an image with many pixels at a low refresh rate or a rough image at a high refresh rate.